Chapter 4 - Propellers to Jets: The Impetus of World War II

A Sixteen-foot Twin on the East Coast


[36] Following the war-stimulated congressional authorization, Langley began expanding into its new West Area in November 1940. Langley already had an 8-foot high-speed wind tunnel in operation, but it was too small for many engineering problems cropping up on new military aircraft-especially where the propulsion system had to be tested. Consequently, plans for the construction of a twin of the Ames 16-foot high-speed tunnel were approved. It had to be a lower- speed version of the Ames facility for the simple reason that Langley did not have sufficient electrical power to run it any higher than Mach 0.7. However, the tunnel's awesome size opened up new research horizons.

The 16-foot tunnel, in fact, was perfect for solving the cooling problems being encountered with aircooled aircraft engines. With few exceptions, most U.S. fighters and bombers in the air and in development [37] depended on air-cooled engines. For every horsepower delivered to the propeller shaft, roughly 2 horsepower of waste heat had to be removed by cooling air flowing past the engine fins and through the exhaust system. True, these engines could be tested on the ground and even in actual flight. But ground testing did not duplicate high-speed airflow into and out of the engine nacelle, and flight testing was costly, time consuming, and very limited in terms of onboard instrumentation. In the 16-foot tunnel, subsonic high-speed flight conditions could be duplicated quickly and cheaply. Full-size engines were mounted in the tunnel and operated at various power levels while hundreds of thermocouples measured temperatures at critical spots. When hot spots were discovered, the cowling and internal baffling could be modified on the spot. New tests could be run immediately, in contrast to long drawn-out flight tests. Wind tunnel testing played a major role in the resounding success of American air-cooled aircraft engines during the war.

Far from being limited to power plant testing, the 16-foot tunnel also tested high-speed propellers and even the shapes of the first atomic weapons. It was not the biggest or fastest NACA wind tunnel, but it was important. In later years, this tunnel was increased in power (see Chapter 5).